ALLPCB
Energy storage inverters are grid-connected inverters designed for the energy storage segment of smart grid construction. They are characterized by bidirectional conversion and a set of specialized capabilities. The energy storage segment of a smart grid can effectively manage power resources, balance diurnal and seasonal load variations, smooth supply and demand differences, and help maintain grid stability.
Four common functions of energy storage inverter systems
1. Unbalanced output
In regions where residential supply is three-phase, three-phase PV energy storage systems are often used in places such as parking lots, stations, and shopping centers. To power single-phase loads within such systems, different amounts of energy must be delivered on each phase. This is referred to as the unbalanced output function.
When anti-backfeed measures limit export power on a per-phase basis, unbalanced output capability becomes essential because the export power for each phase will be constrained independently. The inverter must therefore be able to output different power levels per phase according to each phase's load consumption.
2. Seamless transfer during outage
Off-grid output capability or backup power capability is an important function of PV energy storage systems, especially where the public grid is unstable or critical household loads require uninterrupted supply. In these situations, the energy storage inverter should provide off-grid output capability and seamless transition from grid-connected to outage operation.
3. Remote control
PV systems typically require long-term, continuous operation and maintenance. With extended warranty periods common worldwide, convenient O&M solutions are important for energy storage inverter systems. Remote control greatly reduces the time and cost of on-site after-sales service.
4. Protocol compatibility
A PV storage system typically integrates batteries, PV modules, inverters, racking, meters, control systems, and other components. Inverter manufacturers cannot supply all required equipment for a complete system. A full PV-storage system may also require additional components for intelligent energy management, including an EMS controller, multifunction smart meters, thermal controllers, and pump controllers, to maximize PV self-consumption or to implement specific load control. Therefore, protocol compatibility between the inverter and these devices is important.
Main functions and performance indicators
- Active power smoothing control mode, suitable for short-term smoothing of intermittent energy output fluctuations.
- Passive power smoothing control mode, accepting dispatch control from the grid and participating in peak shaving and valley filling.
- Integrated charge and discharge design, with selectable charge/discharge strategies according to the storage element characteristics (for example constant-current charge/discharge, constant-power charge/discharge, or automatic charge/discharge).
- Grid-connected operation with automatic or dispatchable reactive power compensation and low-voltage ride-through capability.
- Off-grid operation: independent power supply with adjustable voltage and frequency; multi-unit parallel operation with automatic power sharing among units.
- Provides Ethernet, CAN, and RS485 interfaces and supports open communication protocols to facilitate information exchange between the BMS (battery management system) and monitoring systems.
- Comprehensive protection functions to safeguard the power converter and storage elements under various fault conditions.
The primary role of an energy storage inverter is to enable bidirectional energy transfer between the AC power grid and energy storage batteries. As a bidirectional power converter, it can interface with various DC storage units such as supercapacitor packs, battery packs, and flywheels. It can quickly and effectively smooth fluctuations from distributed generation, improving the grid's ability to accept large-scale renewable generation (wind, PV). It can follow dispatch instructions to absorb or supply peak and valley energy and provide reactive power to improve power quality and economic efficiency. During grid faults or outages, it can form an independent power network to enhance the reliability of load supply.
